Regenerative oxidizers (RO), including regenerative thermal oxidizers (RTO) and regenerative catalytic oxidizers (RCO), use a large mass of media or heat sink, usually ceramic based, to provide a high degree of recovery. Typically, the heat sink media of a regenerative oxidizer is in the form of saddles, glued laminated sheets or extruded honeycomb monoliths. Because of the economic benefits of regenerative oxidizers, a large number of polluted gaseous streams are abated by regenerative oxidizers. In some applications, in addition to volatile organic compounds (VOCs), particulate or condensable matter is also present in the waste gas stream and may accumulate in the heat sink media. If the quantity of these fouling agents is sufficient, then the flow passages through the heat sink media can be compromised, causing loss of efficiency of the regenerative oxidizer, or malfunction. In such cases, either the media is washed or heated to burn or bake off the accumulated matter. The process of burning or baking off contaminants is generally referred to as “bakeout.” In this process, the accumulated matter is oxidized to gases or volatilized to gaseous form or converted to a combination of the two forms.
In a bakeout procedure, the heat sink is gradually heated, using the regenerative oxidizer burner or an outside source, to a temperature at which the deposited matter is oxidized (destroyed) and/or volatilized. In most cases, this procedure is performed under an “offline” condition, wherein the regenerative oxidizer is not abating the polluted waste gas stream or is in a maintenance mode. This often implies down time for the process to which the regenerative oxidizer is applied and hence loss of production time. A more preferred procedure would be to carry out the bakeout in an online condition, while processing polluted gaseous streams.
U.S. Pat. No. 6,203,316 assigned to a predecessor in interest of the assignee of this application discloses a proposed continuous online smokeless bakeout process for rotary oxidizers, which is one type of regenerative oxidizer, having a rotary valve as described further below. This patent proposes to operate the rotary oxidizer in a normal manner, but to add heat to the purge gas using a burner. However, testing of the bakeout process disclosed in this patent indicated that the residence time of the heated purge gas is insufficient to burn off accumulated non-volatile contaminants from the heat sink media using the method described in the above-referenced U.S. Pat. No. 6,203,316. Further, it is not possible to simply hold the position of the rotary valve for a time sufficient for bakeout or burn-off of the accumulated non-volatile contaminants without compromising the efficiency of the rotary regenerative oxidizer, because it has been found that bakeout of the accumulated non-volatile contaminants takes between ten to ninety minutes or more preferably about fifty minutes. Thus, a need continues for a method of cleaning the heat sink media of a rotary regenerative oxidizer of accumulated contaminants while continuing operation of the rotary regenerative oxidizer.